Wireless networks serve many purposes. In some cases they are used as cable replacements and in other cases they are used to provide access to corporate data remotely. Industry and technology have enabled these networks to be already valid and not just in limited regions. Mobile communication systems are the most important form of wireless communication today. However, in addition to them, there are other forms of wireless communication that are also important. Table 1 shows the types of wireless networks ranked according to their speed and coverage space.
Short and medium range networks are very interesting for mobile device clients. As users move around carrying mobile devices they need an effective way of communicating and what could be simpler than a wireless network.
Application developers don’t have to worry about internal details of wireless networking to be successful, but they do need some basic knowledge of how these technologies work.
In addition, familiarity with them raises a foundation on which the applications of mobile applications can be based. For example, if the architect of an application knows that the wireless network offers a speed of only 9.6 Kbps then it would limit the frequency and amount of data transmitted. The same discussion can be made about coverage and cost issues.
5.1 WIRELESS LAN
In this section, we focus on LAN wireless technology: IEEE 802.11 LAN wireless, sometimes called wireless Ethernet. To meet the growing needs for this type of technology, companies have launched a wide range of WLAN products. These products usually implement one of the many existing WLAN standards but have recently launched products that support two more standards. WLAN networks are one of the fastest growing areas in the telecommunications industry. WLAN solutions are now implemented in offices, homes, large corporations, factories, public places such as airports, shopping malls, hotels and even bars. In some cases WLAN technology is used to save and avoid cable extensions, in other cases it is the only solution to provide the public with quick Internet access. Whatever the reason, WLAN networks are appearing everywhere in populated environments.
To evaluate a WLAN product, the following issues must be considered:
• Coverage. WLAN products have a coverage area of 50 to 150 m.
• Data transmission speed. Data transfer speeds range from 1Mbps to 54 Mbps.
• Interference. Some of the standards may be affected by interference, which is usually caused by home electronics or other wireless technology.
• Energy consumption. The amount of energy consumed by the wireless adapter varies from one product to another and often depends on the standard that is implemented.
• Cost. The cost of a wireless solution can vary significantly depending on the requirements and standard implemented.
5.2 WLAN Standards
WLAN standards are promoted by IEEE, ETSI (European Telecommunications Standards Institute) and HomeRF.
The IEEE 802.11 specification is the first approved standard. It uses the same protocols as Ethernet but communicates using 2.4 GHz radio frequency. Modulation techniques are FHSS and DSSS. 802.11 products are no longer sold because they have been replaced by improved versions 802.11a and 802.11b which have higher speeds and lower costs.
802.11b / Wi-Fi
It is the most popular 802.11x family standard.
The fact that the 2.4GHZ spectrum is cheaper than the 5GHz spectrum that uses 802.11a makes version b more widespread.
Another advantage of this spectrum is that it can overcome physical barriers better than any other standard. Despite these, this spectrum also has a negative aspect related to frequency overcrowding. Since 2.4 GHz is a frequency that does not require licensing, everyone is free to use it for communication. For example, it can be used from fixed wireless phones or microwave ovens.
This standard reaches a maximum capacity of up to 11 Mbps, which exceeds the speed of 10 Mbps of Ethernet. For this reason it is very convenient to use it for cable network expansion. However, during the implementation it should be taken into account that with the increase of the distance beyond 30 m the signal is weakened.
Security at 802.11b standard
When IEEE created the 802.11 specification, it also implemented an element called WEP (Wired Equivalent Privacy) in order to provide basic data encryption and authentication levels. WEP provides a level of security in WLAN. This is very important because wireless networks do not have the physical protection that cable environments can have. WEP is used by both 802.11a and 802.11b.
To authenticate an access point, it sends a request to the client text in order to identify its identity. The client uses RC4 encryption with a secret key and encrypts the text. He sends this encrypted text back to the access point. As soon as the latter takes the encrypted text, it decrypts it using the same key. If the text matches the text sent then the client is successfully authenticated and given access to the network.